The present invention relates to a ferrule of a connector for single-mode optical fibers with polarization maintenance: that is, optical fibers comprising an elliptical core inside a circular section optical shaft. If necessary, both sides of the elliptical core have constraint elements that exercise an internal asymmetrical constraint on the core or an additional circular core surrounded by an elliptical constraint element.
Such fibers are currently used, for example, in the fabrication of sensors, such as those in high-sensitivity interferometers that require a stable state of linear polarization.
Such fibers are also intended for use in telecommunications systems at very high transmission band.
In connecting these complex fibers, the principal axes of the elliptical core or the elliptical constraint element surrounding the circular core must be aligned in order to decrease connection losses and, above all, to avoid disturbing the polarization state.
The filing company has already described, in EP-A- No. 0063085, a connector for optical fibers that comprises two male ferrules attached to the end of each of the connected fibers, and a female access coupler pierced lengthwise to support and align the two ferrules face to face.
In the central part of the female coupler, inside its lengthwise pierced hole, is a thrust bearing body for the male ferrules. The thrust bearing body has a transverse axial orifice and, around this, a contact projection opposite each of the male ferrules. Each male ferrule has an axial tubular protuberance that can be inserted into the orifice of the thrust bearing body and a conduit into which the optical fiber can be introduced loosely and immobilized in such a way that its end coincides with the end of the protuberance. Each of the ferrules, moreover, has an annular groove set back from the protuberance and surrounding the back part of the latter. The wall of the groove defines a projection of contact with the projection opposite the thrust bearing body of the female coupler under the action of longitudinal means of pressure. The projections opposite the thrust bearing body and each of the male ferrules are arranged in such a way that during any relative movement of the projections in contact, the end of a fiber at the level of the end of the protuberance of a male ferrule will remain at a predetermined, constant distance from the center of the thrust bearing body. The thrust bearing device is preferably a sphere, and the annular groove of each male ferrule has a wall that is conical in profile.
The present invention proposes to produce a male ferrule for a connector of this type, having the general characteristics of the aforementioned ferrules and suitable for cooperating with an access coupler of the type described above to more specifically connect single-mode optical fibers with polarization maintenance.
For this purpose the ferrule produced according to the present invention comprises a tubular outer body, the front end of which has a groove with a wall that is conical in profile. The outer body contains an inner cylindrical element, inside which an optical fiber can be immobilized, particularly by gluing. The inner element protrudes from the end of the outer body, which has radial holes for inserting devices such as piercers for mechanically centering the inner element inside the outer body. The ferrule is characterized by a socket attached in rotation around the body and by means for immobilizing said socket, preferably by gluing, on said body. In addition, the socket is equipped with an indexing reference.
Preferably, the indexing reference consists of a groove through which the ferrule can be inserted onto a corresponding peg in the female access coupler of the connector by placing the ferrule in the access coupler while maintaining the angular position of the fixed fiber, as will be explained later.
To immobilize the inner element containing the optical fiber in the outer body of the ferrule, the ferrule produced according to the invention should have the characteristics described in EP-A- No. 0165837. Thus, the inner groove of the outer body may have, in the area of the radial holes for inserting the piercers, a flat projection perpendicular to its longitudinal axis and a rigid nucleus positioned and immobilized around the inner element. The nucleus comprises a flat projection perpendicular to the longitudinal axis of the element and peripheral projection arranged opposite the radial holes of the outer body. An elastic axial support is exercised on the nucleus, causing the flat projections of the outer body and those of the joined nucleus of the inner element to press in mutual contact.
The elastic support should be carried out via a helical compression spring supported on one end by a projection of the nucleus, parallel and axially opposite said flat projection, and on the other end, by a wall constituting the back of the groove of the outer body. According to the invention, said back wall is formed on an obturation piece of the back of the body inserted into the body and equipped with a longitudinal conduit for passing the fiber and with at least one radial hole, whose use will be explained below. The hole(s) should be suitable for filling with a resin.
In order to center the fiber in the ferrule, as described in EP-A- No. 0063085 and EP-A- No. 0165837, the fiber is illuminated with a white light through the hole in the obturation piece inserted into the back of the body, while the ferrule is held opposite a telescope equipped with a crossbar-shaped reticule.
Thus, by using piercers inserted into the radial holes of the body, the center of the elliptical fiber core or the circular fiber core surrounded by the elliptical constraint element is brought to coincide with the center of the crossbar of the telescope opposite which the ferrule has been placed. Then, according to the present invention, the fiber core is angularly oriented by relative rotation of the crossbar surrounding the body. The large axis of the elliptical core or the elliptical constraint element surrounding the circular fiber core is thus brought to coincide with the desired horizontal or vertical axis of the crossbar, after which the socket on the outer body of the ferrule is immobilized by gluing with resin injected into the radial orifice(s) provided for that purpose. The resulting angular position of the fiber in the body of the ferrule is effected by the indexing groove, which now can be inserted onto the corresponding peg of the access coupler, when the ferrule is inserted into the access coupler. The resulting polarization of the fiber effected for both ferrules of a single connector will be maintained in the connection.